Auxiliary power supply for a welding machine

ABSTRACT

A electric welding machine having an auxiliary power output, and a method for controlling the auxiliary power output on a welding machine is provided. In one embodiment, the system includes a main transformer having a first secondary winding in circuit communication with a welder power output and a second secondary winding in circuit communication with an auxiliary power supply having an auxiliary power output. The auxiliary power supply includes an input for monitoring the welder power output to determine if the welder power output is on; circuitry for determining whether a surge or spike in demand is present at the auxiliary power output; and circuitry for limiting the available power to the auxiliary power output if certain conditions are satisfied. One method includes monitoring the demand on an auxiliary power output, monitoring a welding power output, determining whether there is a spike in the demand on the auxiliary power output that is above a first limit, and reducing the available power to the auxiliary power output if the spike is above the first limit and the welding power output is energized.

This application is a continuation of U.S. patent application Ser. No.12/552,782 filed Sep. 2, 2009 and issued as U.S. Pat. No. 8,426,772,entitled AUXILIARY POWER SUPPLY FOR A WELDING MACHINE, the entiredisclosure of which is fully incorporated herein by reference in itsentirety.

FIELD

Embodiments of the present invention relate generally to weldingmachines, and more specifically to auxiliary power supplies for weldingmachines.

BACKGROUND

Electric arc welders are used in numerous industries, back yard shopsand countries outside of the United States, each of which may have adifferent power source available. Such power supplies may range from 200VAC to 600 VAC, may have a frequency of 50 Hz or 60 Hz, and may be threephase or single phase. Lincoln Electric has developed novel three stagepower sources for electric arc welders that allows the welder to operatewith any of these power supplies. Often the operator has a need to use apower tool, or other device that operates on 115 VAC and no such powersource is available.

SUMMARY

An electric welding machine with an auxiliary power supply is provided.In one embodiment, the available power to the auxiliary power supply islimited if there is a surge or spike in the current draw that exceeds aset limit. In one embodiment there are two surge or spike limits, alower spike limit that triggers a reduction in available power if thewelder output is on, and a higher spike limit that triggers a reductionin available power if the welder output is off. In one embodiment, anelectric welding machine includes an input for receiving a voltage ofbetween about 200 and 600 volts AC. The input is in circuitcommunication with an AC to DC converter, an inverter and a maintransformer that provides isolation from the input. The main transformerincludes a first secondary winding in circuit communication with awelder power output and a second secondary winding in circuitcommunication with an auxiliary power supply having an auxiliary poweroutput. The auxiliary power supply includes an input for monitoring thewelder power output to determine if the welder power output is on, apulse width modulation circuit for providing a pulsed input to a filter,and an input for monitoring the output of the auxiliary power output.The pulsed input to the filter provides a maximum available auxiliarypower output under normal conditions and reduces the available auxiliarypower output if there is a surge or spike on the auxiliary power output.

In another embodiment, the electric welder has at least one transformerfor providing a first reduced AC voltage to a welding power supplyhaving a welding output and a second reduced AC voltage to an auxiliarypower supply having an auxiliary output. The auxiliary power supply mayinclude a rectifier for converting the second reduced AC voltage to a DCvoltage, switches for intermittently providing a positive DC voltage toa first filter input, such as, for example, the inductor of an LCfilter, and a negative DC voltage to a second filter input, such as, forexample, the capacitor of the LC filter, and for intermittentlyproviding a negative DC voltage to the first filter input and a positiveDC voltage to the second filter input. The auxiliary power supply mayinclude control circuitry operating at a frequency of greater than about20 kHz for pulsing the switches to provide variable pulse widths to thefilter. The filter provides an AC power output having a substantiallysinusoidal wave form when a first pulse width is applied to the filter.

In one embodiment a method for controlling an auxiliary power output ona welding machine is provided. The method includes monitoring the demandon an auxiliary power output, monitoring a welding power output,determining whether there is a spike in the demand on the auxiliarypower output that is above a first limit, and reducing the availablepower to the auxiliary power output if the spike is above the firstlimit and the welding power output is energized.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and a more thorough understanding of theinvention may be achieved by referring to the following description,taken in conjunction with the drawings, wherein

FIG. 1 is an exemplary block diagram of a welder having an auxiliarypower supply according to an embodiment of the invention;

FIG. 2 is an exemplary block diagram of an auxiliary power supply for awelder according to an embodiment of the invention;

FIG. 3 is an exemplary diagram of a voltage signal applied to the inputof the filter in an auxiliary power supply for a welder according to anembodiment of the invention;

FIG. 4 is an exemplary diagram of the output voltage signal thatcorresponds to the voltage signal applied to the input of the filter inan auxiliary power supply of FIG. 3;

FIG. 5 is an exemplary diagram of a voltage signal applied to the filterin an auxiliary power supply for a welder according to an embodiment ofthe invention;

FIG. 6 is an exemplary diagram of the output voltage signal thatcorresponds to the voltage signal applied to the input of the filter inan auxiliary power supply of FIG. 5;

FIG. 7 is an exemplary diagram of a voltage signal applied to the filterin an auxiliary power supply for a welder according to an embodiment ofthe invention;

FIG. 8 is an exemplary diagram of the output voltage signal thatcorresponds to the voltage signal applied to the input of the filter inan auxiliary power supply of FIG. 7; and

FIG. 9 is an exemplary flow chart of a logic diagram in accordance withone embodiment of an electric welder having an auxiliary power supply.

FIG. 10 is another exemplary flow chart of a logic diagram in accordancewith one embodiment of an electric welder having an auxiliary powersupply.

DETAILED DESCRIPTION

The following includes definitions of exemplary terms used throughoutthe disclosure. Both singular and plural forms of all terms fall withineach meaning Except where noted otherwise, capitalized andnon-capitalized forms of all terms fall within each meaning:

“Circuit communication” as used herein indicates a communicativerelationship between devices. Direct electrical, electromagnetic, andoptical connections and indirect electrical, electromagnetic, andoptical connections are examples of circuit communication. Two devicesare in circuit communication if a signal from one is received by theother, regardless of whether the signal is modified by some otherdevice. For example, two devices separated by one or more of thefollowing—amplifiers, filters, transformers, optoisolators, digital oranalog buffers, analog integrators, other electronic circuitry, fiberoptic transceivers, or even satellites—are in circuit communication if asignal from one is communicated to the other, even though the signal ismodified by the intermediate device(s). As another example, anelectromagnetic sensor is in circuit communication with a signal if itreceives electromagnetic radiation from the signal. As a final example,two devices not directly connected to each other, but both capable ofinterfacing with a third device, for example, a CPU, are in circuitcommunication. Also, as used herein, voltages and values representingdigitized voltages are considered to be equivalent for the purposes ofthis application and thus the term “voltage” as used herein refers toeither a signal, or a value in a processor representing a signal, or avalue in a processor determined from a value representing a signal.

“Signal”, as used herein includes, but is not limited to one or moreelectrical signals, analog or digital signals, one or more computerinstructions, a bit or bit stream, or the like.

“Logic”, synonymous with “circuit” as used herein includes, but is notlimited to hardware, firmware, software and/or combinations of each toperform a function(s) or an action(s). For example, based on a desiredapplication or needs, logic may include a software controlledmicroprocessor or microcontroller, discrete logic, such as anapplication specific integrated circuit (ASIC), or other programmedlogic device. Logic may also be fully embodied as software. The circuitsidentified and described herein may have many different configurationsto perform the desired functions.

The values identified in the detailed description are exemplary and theyare determined as needed for a particular welder design. Accordingly,the inventive concepts disclosed and claimed herein are not limited tothe particular values or ranges of values used to describe theembodiments disclosed herein.

FIG. 1 is an exemplary block diagram of an embodiment of a welder 100having an auxiliary power supply 170 in accordance with one embodimentof the present invention. Welder 100 may include an AC to DC converter110, which includes an input 105 for receiving AC power. AC to DCconverter 110 is configured to receive a “universal” voltage, such as,for example, voltages that range from about 200 to about 600 VAC andvoltages that may be either three phase or single phase, 50 Hz or 60 Hz.The output of AC to DC converter 110 is in circuit communication with DCbus 115, and preferably, provides an output of about 400 VDC, and DC bus115 is in circuit communication with inverter 120. Inverter 120 convertsthe 400 VDC signal into a 400 VAC, 50 kHz signal which is in circuitcommunication with the primary winding 135 in main power supplytransformer 130. Main power supply transformer 130 has a secondarywinding 140 that is in circuit communication with rectifier 162 inwelding power supply 160. The primary winding 135 and secondary winding140 may have a 4:1 ratio. Accordingly, the 400 VAC, 50 kHz input signalto the main power supply transformer 130 is converted to a 100 VAC, 50kHz input to rectifier 162 of welding power supply 160. For additionalinformation with respect to exemplary embodiments of the above describedcircuitry, see U.S. patent application Ser. No. 11/087,179, filed onMar. 24, 2005, published on Sep. 28, 2006 as U.S. Pub. No. 2006/0213890and is assigned to Lincoln Global, Inc, which is incorporated byreference herein in its entirety. This is but one example of manydifferent welding power supplies that may be used. The inventiveconcepts disclosed herein are not limited to a welding machine having auniversal input voltage.

Main power supply transformer 130 includes another secondary winding 145which is in circuit communication with rectifier 205 (FIG. 2) in theauxiliary power supply 170. The primary winding 135 and secondarywinding 145 may have a 2:1 ratio. Accordingly, the 400 VAC input to themain power supply transformer 130 is converted to a 200 VAC, 50 kHzinput to rectifier 205 in auxiliary power supply 170. The main powersupply transformer 130 is energized when the welder is powered upregardless of whether or not the welder output 165 is on or off.Accordingly, power for the auxiliary power supply 170 is alwaysavailable when the welder 100 is powered on. The additional secondarywinding 145 eliminates the need for an additional transformer, and canbe added to all welding machines at little cost regardless of whether ornot the eventual customer orders the optional auxiliary power output.Another advantage of this embodiment is that the main transformerprimary bus is independent of the welder 100 input voltage 105,accordingly the secondary winding 145 is also independent of the inputvoltage 105. Thus, there is no need to reconnect, or change settings onauxiliary power supply 170 for different ranges of voltage inputs 105.Auxiliary power supply 170 may be offered as an option on the welder100, and in one embodiment, may optionally be provided for customers toinstall after the original purchase if the original welder has theadditional secondary winding 145. Optionally, however, a second inverterand transformer (not shown) could be used to power the auxiliary powersupply, and can be connected to the DC bus 115.

FIG. 2 illustrates an exemplary embodiment of an auxiliary power supply170. Auxiliary power supply 170 is configured to receive an AC input,such as, for example, the aforementioned 200 VAC, 50 kHz signal, whichis rectified by rectifier 205 to provide about a 200 VDC output. Thepositive leg of the 200 VDC output is in circuit communication with bus210 a and the negative leg is in circuit communication with bus 210 b.Bus 210 a is in circuit communication with paired switches SW1 and SW3and bus 210 b is in circuit communication with paired switches SW2 andSW4. The output of SW1 and SW4 are in circuit communication with oneinput of filter 230, such as, for example, the inductor 231 and theoutput of SW2 and SW3 are in circuit communication with the secondinput, such as, for example, the capacitor 232 of filter 230. SwitchesSW1, SW2, SW3, and SW4 are controlled by control circuit 250. Controlcircuit 250 also receives an input signal 255 from the filter output240. Input signal 255 may be, for example, a current or voltage signal.Input signal 255 provides a feedback signal that may be used todetermine one or more of the voltage, ripple, current draw, etc. In oneembodiment, input signal is an analog voltage signal that is received bycontrol circuit 250 which monitors the output voltage and voltageripple.

Switches SW1, SW2, SW3, and SW4 are energized in alternate sequence bygating pulses on lines 220 a, 220 b, 220 c and 220 d. Control circuit250 turns alternate pairs of switches “on” and “off” at a highfrequency, such as, for example, at about 20 kHz or above, and in oneembodiment at about 75 kHz. For example, control circuit 250 may pulseswitches SW1 and SW2 “on” a number of times to create a series ofpositive voltage pulses, such as, for example, pulses 305 (FIG. 3), andthen control circuit 250 may pulse switches SW3 and SW4 “on” a series oftime to create a series of negative pulses, such as, for example, pulses310. This process is repeated creating a series of positive pulsesfollowed by a series of negative pulses. In one embodiment, the pulsewidths increase and decrease to at least partially create thesubstantially sinusoidal output illustrated in FIG. 4. For example,pulses 305 and 310 may include one or more first pulse widths 305 a and310 a respectively, one or more wider pulse widths 305 b, and 310 b, andone or more widest pulse widths 305 c and 310 c. Thus, the positivepulse widths 305 increase from 305 a to 305 b to 305 c and decrease from305 c to 305 b to 305 a corresponding to the sinusoidal wave form ofFIG. 4. Similarly, negative pulse widths increase from 310 a to 310 b to310 c and decrease from 310 c to 310 b to 310 a corresponding to thesinusoidal wave form of FIG. 4. (For simplicity only three differentwidths of pulses are illustrated, however any desired number ofdifferent pulse widths may be used). These voltage pulses are applied tothe input of filter 230. Filter 230 contains an inductor 231 and acapacitor 232, thus, the current and voltage output of filter 230 cannotchange instantaneously. Accordingly, the output of filter 230 is asinusoidal output as illustrated in FIG. 4. The filter 230 componentsmay be selected to generate, for example, a 115 VAC, 60 Hz output.Preferably the output has minimal voltage ripple of, for example, lessthan about 5% of total output voltage. Control circuit 250 monitorsoutput 240 of the auxiliary power supply 170 using the input signal 255and adjusts the pulsing of switches SW1, SW2, SW3, and SW4 to maintain asubstantially consistent sinusoidal 115 VAC output. Output 240 of Filter230 is in circuit communication with a receptacle located on, forexample, the back panel of the welding machine (not shown).

A sinusoidal output, as opposed to a square wave output, is preferred.Many power tools operate more efficiently on a voltage source with asinusoidal wave form and run hotter when operated on a square wave. Inaddition, some equipment does not operate properly at all on a squarewave form, such as, for example, a radio or television where a squarevoltage wave causes harmonic noise, power tools with solid statevariable speed control, some battery chargers and fluorescent lights.

The primary purpose of the electric welder is to provide quality welds.Since the auxiliary power supply 170 shares the primary DC bus 115 withthe welding output 165, too much current draw by, for example, a powertool, on the auxiliary power output 240 may lower the DC bus 115 andcould affect the welding output if it is on. Accordingly, in oneembodiment, control circuit 250 limits the current available at output240 when the welder is in operation. Control circuit 250 monitorswhether or not the welder is in operation through signal 180. In oneembodiment, signal 180 is energized when the welder output 165 is on.Accordingly, if control circuit 250 detects a voltage on signal 180, thewelder output is on. The available output current may be reduced bynarrowing the pulse width of the voltage input to the filter 230. Forexample, FIG. 5 illustrates a series of positive voltage pulses 505having a first pulse width. (In actual practice, pulse widths 505 mayinclude a number of different pulse widths to aid in creating thesinusoidal output.) At time T1 the welder is put into operation andcontrol circuit 250 narrows the width of the pulses 510, 511 therebylimiting the current available to the input of filter 230. At T2, thewelder is no longer being operated and control circuit 250 widens thewidth of the pulse 506 back to its maximum value. FIG. 6 illustrates theoutput of the filter 230 that corresponds to the input of filter 230. AtT1, the output voltage is clipped, or reduced due to the narrower pulsewidths 510, 511, which limits the power, or current, available at output240. At T2, the pulse widths 506 are widened and accordingly, outputvoltage 240 returns to the maximum setting and the wave form 610 revertsback to a substantially sinusoidal wave form.

In one embodiment, control circuit 250 monitors the voltage, oroptionally the current, at output 240 for demand spikes. Some powertools, such as a grinder for example has a 15 amp peak operating currentbut can have over a 100 amp starting current within 100 microseconds ofstarting the grinder. Such a sudden current draw on the auxiliary poweroutput 240 will lower the DC bus 115 and may effect the welding output165 if it is on. Control circuit 250 monitors the voltage or current atoutput 240 and limits the power available by quickly reducing the widthof the pulse, which limits the peak current as soon as control circuit250 detects a spike that is over a set limit. In one embodiment, two ormore spike limits may be set. For example, a first spike limit may beused when the welder output is on, and a second spike limit may be usedwhen the welder power is off. Switches SW1, SW2, SW3 and SW4 areoperated at a frequency of above about 20 kHz and the pulse width can beadjusted on a pulse-by-pulse basis within a few microseconds ofdetecting a spike that is above a set limit. The set spike limits may bea preselected value, or may be a programmed variable value, such as, forexample, a percentage of the maximum available power.

FIG. 7 illustrates the voltage pulses at the input to filter 230. Inthis embodiment, voltage pulse widths 705 are already reduced becausethe welder is in operation. (Initial reduction in the voltage pulsewidths 705 when the welder is in operation is optional and notrequired). At T3, an operator starts a device, such as a grinder, with ahigh starting current. Control circuit 250 detects the high currentdraw, or voltage drop, and because switches SW1, SW2, SW3 and SW4 arepulsed at a frequency above about 20 kHz, and in one embodiment, atabout 75 kHz, control circuit 250 can detect and limit the pulse width710 within microseconds of detecting a high current draw and furtherlimit the power available at output 240. At time T4, the startingcurrent subsides and the control circuit 250 returns the pulse widths705, 706 to the reduced setting used while the welder is in operation.Accordingly, even if a device having a high starting current isconnected to the auxiliary power output 240, the voltage output 165provided for welding remains generally constant. FIG. 8 illustrates thewave form at the filter output 240. The peak voltage of wave form 800 isclipped because the welder is in operation. Between T3 and T4, the waveform 810 may be substantially linear due to the shortened pulse widths710, or have a small chop in the wave form.

An exemplary flow chart of a logic diagram 900 for an embodiment of thepresent invention is provided in FIG. 9. At block 905 the welder isconnected to a power supply and the main welder power is turned on. Atblock 910, the auxiliary power supply output is on at full power. Adetermination is made at block 915 of whether the welder output is “on”indicating that the welder in use. If the welder output is not on thelogic returns to block 910 and the auxiliary power output remains on atfull power. Another determination is made at block 915 to determinewhether the welder output is on. Optionally, if the welder output is on,the voltage pulse width may be slightly reduced at this time (notshown). Generally, if the welder output is on, a determination is madeat block 925 of whether or not there is a spike in the auxiliary poweroutput demand. A spike may be caused by, for example, initial startingof a power tool, such as, for example, a grinder, which has a largestarting current. If a spike is not present at block 925, adetermination is again made at block 915 to determine whether the welderpower output is on. If the welder power output is still on, adetermination is made at block 925 of whether a spike is present in theauxiliary power output demand. If a spike is detected at block 925, thevoltage pulse width is reduced at block 930. Control reverts to block925 to determine whether a spike is still present and continues to loopuntil a spike is not present. Optionally, the loop may includere-determining whether the welder output is on and whether there isstill a spike in the auxiliary output demand. Still yet, in oneembodiment (not shown), if a spike is present for multipledeterminations at block 935 or a set time limit is reached, the pulsewidths are further reduced. Other combinations of determinations andcontrolling of the pulse widths may be used.

Another exemplary flow chart of a logic diagram 1000 for an embodimentof the present invention is provided in FIG. 10. At block 1005 thewelder is connected to a power supply and the main welder power isturned on. At block 1010, the auxiliary power supply output is on atfull power. At block 1015 a determination is made of whether there is aspike in the auxiliary output demand. If there is not, the auxiliarypower output remains at full power. If a spike is detected at block 1015a determination is made at block 1020 of whether the welder output ison. If the welder output is not on, a determination is made of whetherthe spike is above an upper limit at block 1025. The upper limit may bethe same limit used to determine whether a spike occurred at block 1015,however, preferably, the upper limit used at block 1025 is set higherthan the spike detection limit at block 1015 because the welder poweroutput is not on and a slight dip in the input voltage will not have aneffect on a weld. If the spike is not above the upper limit at block1025 a determination is again made at block 1015 as to whether there isa spike in the auxiliary power output demand. If the spike is above theupper limit at block 1025, the pulse width is reduced to a first reducedpulse width at block 1030 and a determination is made at block 1015 ofwhether there is still a spike in the auxiliary output demand. If atblock 1020 the welder output is on, the pulse width is reduced to asecond reduced pulse width at block 1035 and control returns to block1015 to determine whether there is a spike in the auxiliary power outputdemand. Preferably, the first reduced pulse width is greater than orequal to the second reduced pulse width. The logic returns to block 1015and again determines if a spike is present.

The order in which the process flows herein have been described is notcritical and can be rearranged while still accomplishing the same orsimilar results. Indeed, the process flows described herein may berearranged, consolidated, and/or re-organized in their implementation aswarranted or desired.

While various inventive aspects, concepts and features of the inventionsmay be described and illustrated herein as embodied in combination inthe exemplary embodiments, these various aspects, concepts and featuresmay be used in many alternative embodiments, either individually or invarious combinations and sub-combinations thereof. Unless expresslyexcluded herein all such combinations and sub-combinations are intendedto be within the scope of the present inventions. Still further, whilevarious alternative embodiments as to the various aspects, concepts andfeatures of the inventions—such as alternative materials, structures,configurations, methods, circuits, devices and components, software,hardware, control logic, alternatives as to form, fit and function, andso on—may be described herein, such descriptions are not intended to bea complete or exhaustive list of available alternative embodiments,whether presently known or later developed. Those skilled in the art mayreadily adopt one or more of the inventive aspects, concepts or featuresinto additional embodiments and uses within the scope of the presentinventions even if such embodiments are not expressly disclosed herein.Additionally, even though some features, concepts or aspects of theinventions may be described herein as being a preferred arrangement ormethod, such description is not intended to suggest that such feature isrequired or necessary unless expressly so stated. Still further,exemplary or representative values and ranges may be included to assistin understanding the present disclosure; however, such values and rangesare not to be construed in a limiting sense and are intended to becritical values or ranges only if so expressly stated. Moreover, whilevarious aspects, features and concepts may be expressly identifiedherein as being inventive or forming part of an invention, suchidentification is not intended to be exclusive, but rather there may beinventive aspects, concepts and features that are fully described hereinwithout being expressly identified as such or as part of a specificinvention. Descriptions of exemplary methods or processes are notlimited to inclusion of all steps as being required in all cases, nor isthe order that the steps are presented to be construed as required ornecessary unless expressly so stated.

I claim:
 1. An electric welding machine comprising: a main transformerthat provides isolation from a power input to the welding machine, themain transformer having a first secondary winding in circuitcommunication with a welder power output; and a second secondary windingin circuit communication with an auxiliary power supply having anauxiliary power output operable separate from the welder power output topower a separate electrically powered device, the auxiliary power supplyoutput being in circuit communication with a receptacle disposed on anexternal panel of the welding machine for connection with the separateelectrically powered device; the auxiliary power supply including aninput for monitoring the welder power output to determine if the welderpower output is on; circuitry for monitoring the output of the auxiliarypower output; and circuitry for reducing the available power to theauxiliary power output if there is a surge in power demand on theauxiliary power output that exceeds a set limit and the welder poweroutput is on.
 2. The electric welding machine of claim 1 furthercomprising circuitry for reducing the available power to the auxiliarypower output if there is a surge in power demand that exceeds a secondset limit and the welder power output is off.
 3. The electric weldingmachine of claim 1 further comprising circuitry for initially reducingthe available power to the auxiliary power output if the welder outputis on and further reducing the power to the auxiliary power output ifthere is a surge in power demand that exceeds the set limit.
 4. Theelectric welding machine of claim 1 wherein the auxiliary power supplycomprises a rectifier for converting an AC voltage to a DC voltage; oneor more first switches for intermittently providing a positive DCvoltage to a first filter input and a negative DC voltage to a secondfilter input; one or more second switches for intermittently providing anegative DC voltage to the first filter input and a positive DC voltageto the second filter input; and circuitry operating at greater thanabout 20 kHz for pulsing the one or more first and second switches toprovide variable pulse widths to the filter; the filter providing an ACpower output having a substantially sinusoidal wave form.
 5. Theelectric welding machine of claim 1 further comprising: the power inputon the welding machine being configured for receiving a main powervoltage of between about 200 and 600 volts AC; the power input incircuit communication with an AC to DC converter and an inverter thatprovides power to the main transformer.
 6. The electric welding machineof claim 1 wherein the circuitry for reducing the available power to theauxiliary power output comprises pulse width modulation circuitry forproviding a pulsed input, wherein the width of the pulse input isdecreased to decrease the available power to the auxiliary power output.7. The electric welding machine of claim 6 further comprising circuitryto adjust the pulse widths to maintain a substantially 115 volt 60 Hzsinusoidal output.
 8. The electric welding machine of claim 6 whereinthe pulse width modulation circuitry limits the power available at theoutput of the auxiliary power supply on a pulse-by-pulse basis.
 9. Theelectric welding machine of claim 6 wherein pulse width modulationcircuitry operates at a frequency of above about 20 kHz.
 10. Theelectric welding machine of claim 9 wherein the pulse width modulationcircuitry operates at a frequency of about 75 kHz.
 11. A method forcontrolling an auxiliary power output on a welding machine comprising:monitoring the demand on an auxiliary power output, the auxiliary powersupply output being in circuit communication with a receptacle disposedon an external panel of the welding machine for connection with theseparate electrically powered device; monitoring a welding power output;determining whether there is a spike in the demand on the auxiliarypower output that is above a first limit; reducing the available powerto the auxiliary power output if the spike is above the first limit andthe welding power output is energized.
 12. The method of claim 11further comprising determining whether the spike in the demand on theauxiliary power output is above a second limit and reducing the poweravailable to the auxiliary power output if the spike is above the secondlimit and the welding power output is not energized.
 13. The method ofclaim 11 further comprising further reducing the available power to theauxiliary power output if a spike in the demand on the auxiliary poweroutput extends beyond a predetermined duration.
 14. The method of claim11 further comprising providing power to the welding power output from afirst secondary winding, and providing power to the auxiliary poweroutput from a second secondary winding, wherein the first secondarywinding and the second secondary winding are in the same transformer.15. The method of claim 11 further comprising reducing the availablepower to the auxiliary power output by reducing a voltage pulse width toan output filter.
 16. The method of claim 11 further comprisingmaintaining the output of the auxiliary power output to be asubstantially sinusoidal wave form at about 115 volts and about 60 Hz.17. An electric welding machine comprising: means for providingisolation from a power input to the welding machine; means for supplyingpower to a welder power output; means for supplying power to anauxiliary power supply having an auxiliary power output operableseparate from the welder power output to power a separate electricallypowered device, the auxiliary power supply output being in circuitcommunication with a receptacle disposed on an external panel of thewelding machine for connection with the separate electrically powereddevice; means for monitoring the welder power output to determine if thewelder power output is on; means for monitoring the output of theauxiliary power output; and means for reducing the available power tothe auxiliary power output if there is a surge in power demand on theauxiliary power output that exceeds a set limit and the welder poweroutput is on.
 18. The electric welding machine of claim 17 furthercomprising means for reducing the available power to the auxiliary poweroutput if there is a surge in power demand that exceeds a second setlimit and the welder power output is off.
 19. The electric weldingmachine of claim 17 further comprising means for initially reducing theavailable power to the auxiliary power output if the welder output is onand further reducing the power to the auxiliary power output if there isa surge in power demand that exceeds the set limit.
 20. The electricwelding machine of claim 17 wherein the means for reducing the availablepower to the auxiliary power output comprises pulse width modulationcircuitry for providing a pulsed input, wherein the width of the pulseinput is decreased to decrease the available power to the auxiliarypower output.